The invention relates to tetracyclic benzene derivatives of the formula I ##STR2## in which n is 1 to 7, A is trans-1,4-cyclohexylene, 1,4-phenylene, 3-fluoro-1,4-phenylene or 3,5-difluoro-1,4-phenylene, X is F, Cl, CF.sub.3, --OCF.sub.3 or --OCHF.sub.2, and L, Y and Z are each, independently of one another, H or F.
DE-A 3 734 116 discloses liquid crystals of the formula B ##STR3## The compounds B are distinguished only by moderate dielectric anisotropy, which frequently results in relatively high threshold voltages in mixtures.
Like similar compounds, for example, those known from DE-A 32 11 601, the compounds of the formula I can be used as components of liquid-crystalline media, in particular for displays based on the principle of the twisted cell. See, also, copending application Ser. No. 07/623,385, filed Nov. 19, 1990, claiming priority to DE 39 29 525.7 and DE 39 29 526.5, both filed Sep. 6, 1989, DE 39 29 764.0, filed Sep. 7, 1989, and DE 40 09 907.5, filed Mar. 23, 1990; copending application Ser. No. 07/677,891 filed Apr. 1, 1991, and claiming priority to DE 40 10 447.8, filed Mar. 31, 1990; and PCT International Application No. PCT/EP90/01649, claiming priority of GB 89 22 168.3, filed Oct. 2, 1989, and other foreign applications filed after that date.
The substances employed hitherto for this purpose all have certain disadvantages, for example, excessively high melting points, excessively low clearing points, inadequate stability toward the action of heat, light or electrical fields, inadequate electrical resistance, and excessive temperature dependence of the threshold voltage.
The materials employed hitherto have disadvantages, in particular in displays of the super twist type (STN) having twist angles of significantly greater than 220.degree. or in displays having an active matrix.